Heme-Exposed Pooled Therapeutic IgG Improves Endotoxemia Survival

Abstract

Antibody repertoires of healthy humans and animals contain a fraction of antibodies able to acquire additional polyspecificity following exposure to several biologically relevant redox molecules (free heme, reactive oxygen species, ferrous ions, HOCl, etc.). The physiological role of these "hidden" polyspecific antibodies is poorly understood. Similar to inherently polyspecific antibodies, those with induced polyspecificicty may also have immunoregulatory properties. We have previously shown that a pooled human IgG preparation, modified by the exposure to ferrous ions, acquires the ability to significantly improve survival of animals with polymicrobial sepsis or aseptic systemic inflammation induced by bacterial lipopolysaccharide or zymosan administration. In the present study, we have analyzed the effects of administration of heme-exposed pooled human IgG in the same models of sepsis and aseptic systemic inflammation. The administration of a single dose of heme-exposed pooled IgG has resulted in a significant increase in the survival of mice with endotoxinemia, but not in those with polymicrobial sepsis and zymosan-induced severe generalized inflammation. Finally, we have provided evidence that the anti-inflammatory effect of heme-exposed IgG can be explained by scavenging of pro-inflammatory mediators.

Interaction of clinical-stage antibodies with heme predicts their physiochemical and binding qualities

“…Although the post-translational diversification of the antigen-binding specificity mediated by heme can have contribution to immune defense and immune regulation (24,(29)(30)(31), this phenomenon would be highly undesirable for the therapeutic Abs. The appearance of polyreactivity can decrease potency and represents a risk for side effects due to compromised pharmacokinetics and off-target binding (6,9,32).…”

Enhanced Pro-apoptotic Effects of Fe(II)-Modified IVIG on Human Neutrophils

“…While we observed a net increase of FAS receptor binding activity of IVIG upon ferrous iron exposure, we observed a reduced blocking capacity of IVIG to the monoclonal anti-FAS antibody CH11, suggesting that FAS-mediated death by Fe(II)-IVIG depends on a higher ratio of agonistic vs. blocking anti-FAS antibodies. in vivo studies using murine models of sepsis or autoimmune diabetes demonstrated an increased anti-inflammatory potential of IVIG modified by ferrous ions or heme (21)(22)(23)(24). However, we previously observed that mouse neutrophils are resistant to IVIG-mediated death, suggesting that at least certain in vivo models may not adequately reflect IVIG effects on neutrophils, eventually due to species-differences of epitopes and molecular pathways (15).…”

“…Co-factors, such as ferrous ions, reactive oxygen species and heme have been shown to broaden the specificities of immunoglobulins (19,20). IVIG modified by ferrous ions or heme showed superior therapeutic effects in various in vivo models of sepsis (21)(22)(23) or autoimmune diabetes (24).…”

Breaking the law: unconventional strategies for antibody diversification

“…Efforts have focused on determining the therapeutic effect of antibodies pre-treated in vitro with haem and then administered in models of inflammatory and autoimmune diseases. For example, in contrast to mice injected with native pooled IgG, mice treated with a single dose of IgG exposed to haem were better protected from LPS-induced systemic inflammation 108 . A beneficial role of haem-bound IgG has also been demonstrated in a model of autoimmune diabetes 109 .…”